The human body is totally dependent upon continuous supply of Oxygen (O2) utilized by various tissues and cells in order to transfer energy from food components into the high-energy phosphate molecules named ATP (Adenosine-Tri-Phosphate). Most of the O2 absorbed in the body (>95%) is utilized by the mitochondria (C. L. Waltemath, Oxygen, uptake, transport and tissue utilization, Anesth.Analog. 49 (1970), pp. 184-203), which produces 95% of the ATP in normal tissues, as illustrated in FIG. 1. When O2 supply will be restricted or limited the production of ATP will decrease and as a result, cellular functions will be affected (inhibition of pumping activity for example).
In general terms, when the balance between O2 supply and O2 demand is negative the function of the tissue or organ will be affected and a pathological state is developed. Typical examples to a severe negative O2 balance are heart attack or stroke where due to occlusion of blood vessel in the heart or the brain the supply of O2 to a specific region in the vital organ will be limited and the function will be inhibited. These two examples represent dramatic and acute pathological events and the diagnosis of such conditions is relatively easy and fast. In a large segment of critically ill patients the changes in O2 balance is a slow process developed in one or more areas of the body and may end up in morbidity and mortality in large number of patients. A typical example of such a pathological state is sepsis, which is a major cause of death in many patients hospitalized in intensive care units (ICUs) or even in regular hospital departments.
The Centers for Disease Control (CDC) published data about the dynamic of the population size suffered from sepsis. In 1990 they estimated, in the USA, 450,000 cases of sepsis per year with more than 100,000 deaths (Centers for disease control: increase in national hospital discharge survey rates for septicemia—United States 1979-1987 JAMA. 1990, 263:937-938). In 2001, Angus et al estimated that the number of sepsis patients will grow to 934,000 in 2010, and to 1,110,000 in 2020 (D. C. Angus, W. T. Linde-Zwirble, G. Clermont, J. Carcillo, M. R. Pinsky, demiology of severe sepsis in the United States:Analysis of incidence, outcome, and associated costs of care. 2001, Crit. Care Med., 29:1303-1310). They concluded that “Severe sepsis is a common, expensive and frequently fatal condition, with as many deaths annually as those from acute myocardial infarction”.
Sepsis represents a large group of patient illnesses in which the deterioration of O2 balance is very hard to identify and the consequences in many cases are fatal. The various groups of “slow killing” pathologies (like sepsis) are very hard to diagnose due to lack of specific and sensitive enough techniques or methods. Other examples include hypotension, systemic hypoxemia, or acute Respiratory Distress Syndrome (ARDS). The same problem of O2 imbalance may develop in preterm or full term infants hospitalized in the neonatal ICU or even in the newborn during delivery. The total number of patients suffer annually from shock, trauma and sepsis is 1.5 million with costs above US$50 billion (Ruffolo, 1998).
Body Homeostatic Compensatory Mechanisms
Under mild emergency situations, where body O2 is interrupted, some mechanisms of preserving body homeostasis may take place and may return the body to its steady state conditions. Under moderate or severe O2 imbalance or the development of emergency pathological state, such as sepsis or severe hypotension for example, the body will not be able to compensate completely the deficit of O2.
It is well known and documented that the Autonomic Nervous System (ANS) and mainly its sympathetic branch, including the adrenal gland (secretion of Adrenaline), dominate the compensatory mechanisms of the body related to O2 deficiency. The rapid compensatory reaction to decrease in blood volume (hypovolemia for example), appears in all textbooks of physiology (i.e. W. F. Ganong, Review of Medical Physiology. 1991, pp 578-579, 588-589 Appelton & Lange Medical book). This includes redistribution of blood flow to various organs and giving preference to the most vital organs in the body, namely to the, brain, heart and adrenal glands (A. Barber et al., Shock. In: Principles of surgery. 1994, S. I. Schwartz et al. (Eds.), 7th edition. McGraw-Hill, N.Y., pp. 101-122).
In order to demonstrate the significance of the present invention a typical emergency O2 imbalance in a clinical situation is demonstrated hereinafter. The field of fetal distress or hypoxemia including the monitoring approaches during delivery were reviewed in 2001 by Clerici et al (G. Clerici, R. Luzietti and G. C. Di Renzo, Monitoring of Antepartum and intrapartum fetal hypoxemia: pathophysiological basis and available techniques. Biology Neonate, 2001, 79:246-253.) As they summarized “Due to the limitations of cardiotocography, additional information is required for appropriate decision making during labor. Current evidence suggests that modern technology applied to fetal surveillance can provide useful additional information that can improve our capacity to interpret fetal reaction to labor events”.
Based on Clerici et al and other publications, including the inventors' own research activities, FIG. 2 illustrates the sequence of events that occur under fetal hypoxemia.
Thus, referring to FIG. 2, Placental hypoxia (I) can lead to changes in the delivery of O2 to the fetus and as a result fetal hypoxemia may develop (II). Under this condition (limitation in O2 supply), glycolysis (anaerobic metabolism) will be stimulated and the resulting increased production of lactic acid will be recognized as acidosis (decrease in blood pH). It is well known that under hypoxic conditions the fetus responds to acute or chronic lack of O2 using various mechanisms.
In the acute phase of hypoxia, the fetus will decrease its biophysical activity in order to reduce total body O2 consumption. This may increase O2 supply to vital organs such as brain, adrenals and heart. The activated mechanism of vascular redistribution (III) will decrease blood flow to the kidneys, G-I tract as well as to the peripheral vasculature such as cutaneous and skeletal muscle vessels. This mechanism of redistribution of blood to various organs of the body, called “Brain Sparing Effect”, may lead to “Fetal hemodynamic centralization”. The involvement of higher levels of noradrenaline, due to the increased sympathetic activity (IV), will increase the oxygen delivery to the brain in order to avoid brain damage.
At this point in time there are two possible developments:                A. An appropriate response of the “brain sparing effect” to minimize the effect of hypoxemia on the fetus. If the cause for this condition will be resolved, the fetus will return to so call normal conditions and no damage to the brain will be recognized.        B. The development of a vicious cycle response or cascade of events. Under such conditions the centralization of blood will affect cardiac hemodynamics so that more blood will flow to the brain. During this phase the fetus will present an extreme response to the increasing hypoxemia and the fetal heart function will be impaired. This stage, known as the decompensatory phase may lead to brain damage including edema. The damage may be permanent.        
In order to evaluate, in real time, the hemodynamic and metabolic state of the fetus, during labor, several approaches were developed and applied to clinical usage:                1. Doppler velocitometry of the major arteries, namely, aorta, femoral artery, renal artery or the main arteries supplying the brain. During the initial phase the Doppler technique is not a sensitive tool for detecting changes in the uteroplacental vascular bed or gas exchange and metabolites. It is important to note that Doppler velocitometry is more meaningful during the progression of fetal hypoxemia.        2. Fetal Heart Rate, which may be monitored externally by placing sensors on the mother's abdomen or internally by an electrode attached to the fetal scalp.        3. Uterine Contraction pressure may be monitored by placing a sensor in the uterine cavity or by external monitor.        4. Pulse Oximetry can provide real time values of fetal arterial blood saturation with oxygen (SpO2). The probe is placed between the uterine wall and fetal cheek. The level of SpO2 could be used as a warning signal to fetal hypoxemia.        5. Sampling of scalp blood for the measurement of pH is done whenever fetal hypoxemia is suspected as indicated by the scalp heart rate monitor.        The disadvantage of this approach is that the information obtained is not in real time mode.        
The right side of FIG. 2 shows typical directional changes recorded in the various organs after the sympathetic stimulation. As seen, the blood flow to the brain and the heart increased while the energy state of the non-vital organs is deteriorated. All the possible monitored parameters will indicate this trend although in practice only few parameters were monitored.
Pathophysiology of Critically Ill Patients
The same pattern of pathophysiological cascade of events may occur in many emergency clinical situations in adult patients and may lead to morbidity and mortality. Such situations may include tissue hypoxia, which was discussed in detail during the consensus conference (1996). As shown in FIG. 3, various pathological states may lead to metabolic disturbances and may end up in cellular energy derangement (Hotchkiss and Karl, 1992; Marik and Varon, 1998; Ince and Sinaasappel, 1999; Meier-Hellmann and Reinhart, 1995).
The six pathological states, shown in the left side of FIG. 3, are the most common events that may develop in clinical practice. The states may develop due to specific clear event, such as a major operation such as heart bypass, brain operation, organ transplant, during the operation as well as during the post-operative period, or during slow process of body deterioration, such as in sepsis or shock. The definition of each of those 6 states is not so well established and some overlapping may exist. Under all those situations the metabolic state of the body will be deteriorated and energy failure will develop. In the right side of FIG. 3 the list of clinical situations given include most of the major clinical situations, such as trauma, perinatal, intra-operative period, post-operative period, and internal medicine, typically treated by major hospitals.
As a central protection mechanism, blood flow redistribution will occur and the three protected organs (brain, heart and adrenal gland) will receive more blood and O2, while the peripheral organs or areas (skin and muscles), as well as other non vital visceral organs, will undergo vasoconstriction and a decrease in blood flow and O2 supply will occur.
Monitoring of Critically Ill Patients in Medical Practice
As shown in FIG. 2 and FIG. 3, under various severe pathophysiological conditions the compensatory mechanisms of blood flow redistribution is taking place and as a result the sympathetic stimulation will induce significant decrease in tissue oxygenation in non-vital organs and tissues. Under these conditions the vital organs of the body are protected by preserving high blood flow and O2 supply.
The search for a significant or perfect indicator as well as the most representative organ or tissue in the body to be monitored is an ongoing process. Ince and Sinaasappel (1999) concluded that “To evaluate the severity of microcirculatory distress and the effectiveness of resuscitation strategies, new clinical technologies aimed at the microcirculation will need to be developed. It is anticipated that optical spectroscopy will play a major role in the development of such tools”. In a recent published paper Kruse summarized the effort done, by various investigators regarding the perfect indicator of dysoxia, which could be defined as a state of supply-dependent oxygen consumption (J. A. Kruse, Searching for the perfect indicator of dysoxia, Crit. Care Med. 1999, 27:469-470). It is possible to divide the various existing monitoring devices or parameters according to the monitoring site as shown in FIG. 4. The systemic monitoring site is defined as a parameter represents the cardiovascular, respiratory systems or the circulated blood.
The list of parameters in the local monitoring site is divided into the two groups according to its significant value in keeping the organism alive under severe emergency situations. The monitored parameters listed under low or non vital organs, are divided to those published already in the literature, and the group of parameters included in the MPA (Multi Parametric Approach) which is part of the present invention.
Kruse (1999) suggests that during systemic insults that result in globally diminishing DO2 (Delivery of O2), dysoxia probably manifested in the splanchic region before it can be detected by systemic measurements. In another paper M. P. Fink reviewed the possible involvement of mitochondrial dysfunction in organ failure developed in sepsis (M. P. Fink, Cytopathic Hypoxia: Mitochondrial dysfunction as mechanism contribution to organ dysfunction in Sepsis, Critical Care Clinics. 2001, 17: 219-237). He came to a very important conclusion regarding the type of parameter to be monitored in septic patients. Fink wrote that the effort to improve outcome in patients with sepsis by monitoring and manipulating cardiac output, systemic DO2, and regional blood flow are doomed to failure; instead, the focus should be on developing pharmacological strategies to restore normal mitochondrial function and cellular energetics. Nevertheless, Fink does not suggest that any particular parameters should be monitored to achieve such a goal, less so how to monitor such parameters
The search for an early indication for multiorgan failure is an ongoing process for the last 10 years. Most of the studies were performed in animal experiments. Shoemaker et al. (1984) compared tissue PO2 in conjuctival and transcutaneous areas. Most of the effort was directed toward the development of real time monitoring device for the spelnchnic metabolic state (Fink, 1991; Fiddian-Green and Baker, 1987; Hasibeder et al., 1996). The most recent papers will be cited as follows. Rozenfeld et al. (1996) used PCO2 electrode attached to the mucosal side of the intestine. Sato et al. (1997) measured the same parameter in the esophagus during hemorrhagic shock. They found that esophageal tonometry may serve as a practical alternative to gastric tonometry suggested by various investigators (i.e. Ruffolo, 1998 and Bloechle et al., 1999).
In a rat model Morgan et al. (1997) monitored PCO2 in the ileum during reduction in aortic pressure. In a pig model Knichwitz et al used the intramucosal PCO2 as an indicator to intestinal hypoperfusion.
In order to simplify the monitoring approach Weil et al. (1999), Povas et al. (2001), Marik, (2001), Weil (2000), Schlichtig and Heard (1999), suggested monitoring PCO2 in the sublingual area, which is the most proximal area of the G-I tract. They found that such a measurement could serve as a good indicator to the severity of circulatory shock.
Pernat et al. (1999) and Povas et al. (2000) compared the gastric and sublingual PCO2 as indicators for impaired tissue perfusion. They found similar changes under hemorrhagic shock. In a pig model Puyana et al. (2000) measured abdominal wall muscle. They concluded that pH was the most sensitive site as compared to the stomach or the abdominal wall muscle. Vallet et al. (1994) compared gut and muscle PO2 in endotoxemic dogs. Sakka et al. (2001) assessed the variability of spalachnic blood flow during stable global hemodynamics in septic patients and compared it to gastric tonometry. Boekstegers et al. (1994) measured skeletal muscle PO2 in patients with sepsis. Nordin et al. (1998), Walley et al. (1998) and Dubin et al. (2001) measured intramucosal pH in different segments of the gastrointestinal tract under hemorrhagic shock. The same approach of monitoring gastric PCO2 was used in patients after subarachnoid hemorrhage by Koivisto (2001). The next step was to compare various tissue parameters monitored simultaneously in the skeletal muscle under hemorrhagic shock. Mckinley et al. (1998) monitored PO2, PCO2 and pH in dogs under hemorrhagic shock and also in a patient. Mckinley and Butler (1999) used a fiber optic probe and compared gastric tonometry (PCO2, pH) to muscle PO2, PCO2 and pH in hemorrhagic shock. They concluded that muscle monitoring was more sensitive as compared to gastric tonometry on systemic parameters. To evaluate the changes and severity of blood loss as well as the efficacy of the resuscitation process, Sims et al. (2001) used skeletal muscle monitoring of PO2, PCO2 and pH and found the correlation with the severity of blood loss and resuscitation. The same approach was used in the liver by Soller et al. (2001). In 1995 Powell et al. measured subcutaneous oxygen tension in rats as an indicator of peripheral perfusion. Using the same idea, Venkatesh et al. (1994, 2000) compared subcutaneous PO2 to ileal luminal PCO2 in animal model of hemorrhagic shock, subcutaneous PO2 was more sensitive parameter.
Another approach to monitor organ perfusion outside the G-I tract was described by Rossen et al. (1995). They found that the epithelial PO2 in the bladder was responsive to norepinephrine in a rat model. Rosser et al. (1995) and Singer et al. (1995) used PO2 electrodes in the bladder exposed to sepsis or hemorrhage. Singer et al. (1996) repeated those studies in a model of fluid repletion. Lang et al. (1999) monitored PO2, PCO2 and pH in the bladder during ischemia and reperfusion. Clavijo et al. (2002) monitored pH and PCO2 in the gut as well as in the bladder wall mucosa and found comparable changes in the two organs under shock in a pig model.
Studies in vitro had shown that the urethra was more sensitive to ischemia as compared to the bladder. (Bratslavsky et al., 2001).
Other approaches to monitor HbO2 saturation and cytochrome aa3 redox state were done by various groups in animals as well as in patients (Cairns et al., 1997; Guery et al., 1999 and Mckinley et al., 2000). In patients, Jakob and Takala evaluated the variability of spalanchnik blood flow in patients with sepsis.
In U.S. Pat. Nos. 6,258,046, 6,216,024, devices and methods are described for assessing perfusion failure, by measuring the partial pressure of carbon dioxide (PCO2) in the gastrointestinal tract, or the upper digestive and/or respiratory tract of a patient. In U.S. Pat. Nos. 6,071,237 and 5,579,763 devices and methods are described for assessing perfusion failure, by measuring the partial pressure of carbon dioxide in the lower respiratory tract or the digestive system of a patient. In U.S. Pat. Nos. 6,330,469 and 6,216,032, a method and apparatus are described for early diagnosis of a potentially catastrophic illness in a premature newborn infant, in which the heart rate variability in the infant is monitored continuously, and in which at least one characteristic abnormality in the heart rate variability that is associated with the illness. None of these patents discloses or suggests the parametric monitoring for determining early diagnosis of body metabolic emergency state that may develop in many acute or chronic clinical conditions.
FIG. 5 shows the Hemodynamic and Metabolic responses of 4 different organs to norepinephrine injection, intravenously administered during experiments by Applicant. Measurements were done in the Brain (B), Kidney (K), Liver (L) and Testis (T) by placing a surface optical probe on each one of the 4 organs of a rat. Four different monitored parameters are presented for each organ, namely, Reflectance (Ref), Fluorescence (Flu), Corrected NADH fluorescence (NADH) and microcirculatory blood flow (TBF). The monitoring was done by a 4 channel fluorometer reflectometer (A. Mayevsky & B. Chance, Intracellular Oxidation-Reduction State Measured in Situ by a Multicannel Fiber-Optic Surface Fluorometer. Science, 1982, 217: 537-540) and 4 laser Doppler flowmeters (T. Manor, A. Meilin, & A. Mayevsky. Monitoring different areas of the rat cortex in response to fluid percussion trauma. Israel J Med Sci, 1996, 32, Supplement, S39; A. Mayevsky, A. Kraut, T. Manor J. Sonn, & Y. Zurovsky, Optical monitoring of tissue viability using reflected spectroscopy in vivo. Tuchin, V. V. Optical technologies in biophysics and medicine II. Proceeding of SPIE, 2000, 4241: 409-417 saratov, Russia; A. Mayevsky, A. Meilin, G. G. Rogatsky, N. Zarchin, & J. Sonn, Multiparametric monitoring of the awake brain exposed to carbon monoxide. Journal of Applied Physiology, 1995, 78, 1188-1196). As seen in FIG. 5, the injection of norepinephrine gave a clear preference to brain oxygenation as compared to the “non vita” organ, namely the kidney, liver and the testis. The blood flow (TBF) was dramatically increased while in the other organs TBF decreased significantly. The reflectance showed a clear decrease in the brain due to a vasodilatation response. The fluorescence and the corrected fluorescence (NADH) showed an oxidation in the brain while in the other 3 organs NADH became reduced (increased signal) due to the lack of O2. It is important to note that all parameters were monitored simultaneously in the same animal.
FIG. 6 shows a comparison of the hemodynamic and metabolic responses to ischemia (left side of figure) and adrenaline injection (right side of figure) in the rat brain (B) and skin (S) in the scalp area. Three parameters are presented for each organ, namely, Reflectance (R-B, R-S), NADH redox state (NADH-B, NADH-S) and microcirculatory blood flow (TBF-B, TBF-S). Ischemia was induced by occlusion of the two carotid arteries which provide blood to the two monitored areas. The monitoring devices were used as in FIG. 5 although only two channels were used.
Under occlusion of the two carotid arteries, complete ischemia was induced in the two locations as expected. Under adrenaline, the preference was given to the brain, thus blood flow increased while NADH became more oxidized (decreased signal). In the skin, blood flow decreased to very low values and NADH increased significantly.
In FIG. 7 and FIG. 8 the comparison between brain and the small intestine is shown under anoxia and norepinephrine injection IV. Here again, when the massive insult was affecting the O2 availability in the two locations, at the same time, the responses were similar in terms of mitochondrial function. Under anoxia (FIG. 7), NADH increased in the intestine and the brain while blood flow changes were completely reversed in the two organs. This is a result of the autoregulatory mechanism trying to protect the brain under anoxia by increasing blood flow. When norepinephrine was injected, the preference of the brain was clear as compared to the shut down of blood flow and O2 to the intestine.
The same relationship between brain and small intestine are shown in FIG. 9 and FIG. 10 but the probe was located on the serosal side (outside) of the intestine, while in FIG. 7 and FIG. 8, the measurements were taken in the mucosal side (inside) of the small intestine.
The Significance of Multiparametric Monitoring of Tissue's Pathophysiological State.
It is important to note that the diagnostic value of a real time monitoring system in patients is dependent upon the following criteria:    A. The anatomical site in the body where the monitoring probe is located.    B. The compartment of the tissue of which the monitored parameter is originated, i.e. vascular, extracellular, cytosolic space or intra mitochondrial space. A combination of more than one compartment is also possible.    C. The type of the monitored parameter and its significance in terms of physiological and biochemical processes.
Criterion A
The following monitored anatomical sites were published in various publications:    1. Skin—Transcutaneuous, Sub Cutaneuous, and Conjuctiva.    2. Muscle—Skeletal Muscle, Abdominal wall muscle.    3. Gastro-Intestinal tract—Sublingual, Stomach and Small intestine.    4. Urogenital System—Bladder, Urethra. The difference between various organs is significant in the easiness of anchoring the probe to the tissue and the stability of the measurement. Also, in clinical application of the probe, it is important to attach the probe to other devices.
Criterion B
Most of the parameters monitored and published represent an average of number of tissue compartment mentioned. Tissue PO2, pCO2 or pH are monitored by insertion of the probe to the tissue or by locating the probe on the surface of the tissue. As a result, those three parameters represent the various compartments without any information regarding the relative contribution of each on the compartments. Therefore the results of PO2, PCO2 or pH could be sensitive to other factors in tissue physiology such as blood flow. The measurement of microcirculatory blood flow provides information on the intravascular compartment. This parameter together with the oxygenation level of the HbO2 (Hemoglobin Saturation), that could be measured by visible or NIR spectroscopy, represent the supply of O2 to the examined tissue. Therefore, it is possible to describe the relationship between O2, Supply and Demand in a different but a parallel way as compared to Ruffolo (1998).
Referring to FIG. 11, in A, under normal conditions, the supply of O2 is adequate and meet the demand as that mitochondrial function can be in the normal range (state 4-state 3 range) as described by chance & Williams in 1955. When the supply is diminished to a level that both flow and O2 extraction reached its maximal compensation the critical point reached will induce a decrease in O2 consumption and inhibition of oxidative phosphorylation (B). When the metabolic activity of the tissue/organ is stimulated, both demand and supply will increase (C) and mitochondrial activity will be stimulated to supply the extra ATP needed.
Under hypoxic conditions some organs, like the brain and heart that are autoregulated, supply will increase but mitochondrial activity is partially inhibited (D). Under those conditions, blood flow to the non-vital organs will be diminished and as a result the mitichondrial function will be inhibited. This process of blood flow redistribution is the basic concept, which is the theoretical basis to the current invention.
Criterion C
The various monitored parameters present in FIG. 11 represent various biochemical and physiological processes therefore the significance of each one of them is not identical in terms of early warning of emergency state developed in the body.
The most advanced technology is the monitoring of PCO2 in various organs and mainly in the sublingual location. It is important to note the CO2 is a by-product of the tricarboxlic acid cycle, which generates the NADH, which is later utilized by the mitochondria. The level of CO2 is connected to various other processes, including the body acid-base balance and therefor the interpretation of the changes is dependent on various cellular and tissue activities.
Monitoring of pH has the same problematic disadvantage due to the various processes taking place in the acid-base balance. Two other parameters, PO2 and HbO2 are sensitive to blood flow and are not regulated processes. Both of them are dependent parameters and therefore are less sensitive to the significant metabolic processes. The other two parameters, TBF and mitochondrial NADH (Fp) are the most regulated processes and the relationship between them can vary in different pathological situations. Therefore monitoring each one of them alone is not sufficient due to coupling or uncoupling processes between the two parameters. Under decrease perfusion developed under hemorragic shock will always lead to an increases in the NADH levels in the mitochondria due to the lack of O2. But those two parameters may behave differently during recovery processes, which are the most significant stages in diagnosis of the prognosis of the patient after acute emergency state.
In many instances blood flow will recover to the large blood vessels as well as to the microcirculation but the mitochondria will still be inhibited. Such conditions may be recorded under the development of pathological states such as sepsis or during recovery from hemorragic shock.
Therefore, and according to the present invention, for good diagnosis of a patient, multiparametric monitoring of the most regular processes in the tissue is necessary. Also, the quantification of the metabolic state of the organ, using optical techniques, namely, TBF and mitochondrial redox state, is practical under the multiparametric monitoring.
Due to the regulation of blood flow to various organs and the redistribution of TBF to the vital organs versus the non-vital organs, it is very clear that the entire organ will be regulated and the responses will be very similar in each part of the organ. Therefore it is not necessary to monitor all the parameters from the same volume of tissue. For this reason the various probes that monitor the various parameters could be separated from each other and the diagnosis will be valid.
As can be seen in FIG. 12, the urethra is very sensitive to sympathetic stimulation. Adrenaline was injected at time 0 and TBF decreased immediately to very low levels, together with an increase in NADH levels, due to a significant decrease in O2 supply. The recovery to the normoxic level was very slow and a clear correlation between TBF and NADH can be seen.
Multiparametric Monitoring
Mammalian tissues are dependent upon the continuous supply of metabolic energy (such as ATP and phosphocreatine) in order to perform their various vital activities such as biosynthesis, ion transport and the like. Because the changes in tissue energy metabolism may have a transient nature or may be permanent, to assess the tissue energy-state, it is necessary to monitor the events continuously using a real-time system.
There is a direct correlation between energy metabolism of the cellular compartment and the blood flow in the microcirculation of the same tissue. In a normal tissue, any change in the O2 demand will be compensated by a corresponding change in the blood flow to the tissue. By this mechanism, the O2 supply remains constant if there is no change in the O2 consumption. A change in blood flow will change the apparent energy state, so there is a significant correlation between the decrease in flow (increased ischemia) and the increase in NADH levels.
The parameters commonly used in the art for the assessment of tissue vitality include: A—Blood Flow Rate; B—Mitochondrial Redox State or the NADH Level; C—Blood Oxygenation State; D—Blood Volume; and E—Flavoprotein Concentration
A—Blood Flow Rate
The blood flow rate relates to the mean volume flow rate of the blood and is essentially equivalent to the mean velocity multiplied by the number of moving red blood cells in the tissue. This parameter may be monitored by a technique known as Laser Doppler Flowmetry, which is based on the fact that light reflected off moving red blood cells (RBC) undergoes a small shift in wavelength (Doppler shift) in proportion to the cell's velocity. Light reflected off of stationary RBC or bulk stationary tissue, on the other hand, does not undergo a Doppler shift.
By illuminating with coherent light, such as a laser, and converting the intensities of incident and reflected light to electrical signals, it is possible to estimate the blood flow from the magnitude and frequency distribution of those signals (Stern 1975, U.S. Pat. No. 4,109,647).
B—Mitochondrial Redox State or the NADH Level
The level of NADH, the reduced form of NAD, is dependent both on the availability of oxygen and on the extent of tissue activity. Referring to FIG. 13(a), whilst NADH absorbs UV light at wavelengths of about 310-400 nm and fluoresces at wavelengths of about 430-490 nm, the NAD does not fluoresce. The NADH Level can thus be measured using Mitochondrial NADH Fluorometry. The conceptual foundations for Mitochondrial NADH Fluorometry were established in the early 1950's and were published by Chance and Williams (Chance & Williams, 1955). They defined various metabolic states of activity and rest for in-vitro mitochondria.
An increase in the level of NADH with respect to NAD and the resulting increase in fluorescence intensity indicate that insufficient Oxygen is being supplied to the tissue. Similarly, a decrease in the level of NADH with respect to NAD and the resulting decrease in fluorescence intensity indicate an increase in tissue activity.
C—Blood Oxygenation State
The blood oxygenation state parameter refers to the relative concentration of oxyhaemoglobin to deoxy-haemoglobin in the tissue. It may be assessed by the performance of photometry measurements. The absorption spectrum of oxy-haemoglobin HbO2 is considerably different from the absorption spectrum of deoxy-haemoglobin Hb (Kramer & Pearlstein, 1979). The measurement of the absorption at one or more wavelengths can thus be used to assess this important parameter. Blood oximeters are based on measurement of the haemoglobin absorption changes as blood deoxygenates (Pologe, 1987). Such oximeters generally use at least two light wavelengths to probe the absorption. In these devices one wavelength is at an isosbestic point while the another wavelength is at a point that exhibits absorption changes due to variation in oxygenation level.
For monitoring the oxygenation levels of internal organs, fiber-optic blood oximeters have been developed. These fiber-optic devices irradiate the tissue with two wavelengths, and collect the reflected light through the optical fibers. By analysis of the reflection intensities at several wavelengths the blood oxygenation is deduced. The wavelengths used in one such system were 585 nm (isosbestic point) and 577 nm (Rampil et al., 1992). Another blood oximeter measures and analyzes the whole spectrum band 500-620 nm (Frank and Kessler, 1992).
The commercial pulse oximeters measure oxygenation of arterial blood rather then blood oxygenation in the tissue. These instruments utilize artery pulsation in order to extract absorption changes originated in arterial blood.
The wavelengths used in commercial pulse oximeters are typically around 660 nm in the red region of the spectrum, and between 800 to 1000 nm in near-infrared region (Pologe, 1987).
D—Blood Volume
The blood volume parameter refers to the concentration of the blood in the tissue. When tissue is irradiated, the intensity of reflectance ‘R’, at the excitation wavelength, from the tissue is informative of the blood volume. The intensity of the reflected signal, R, also referred to as the total backscatter, increases dramatically as blood is eliminated from the tissue as a result of the decrease in haemoglobin concentration. Similarly, if the tissue becomes more perfused with blood, R decreases due to the increase in the haemoglobin concentration. The excitation wavelength for R parameter is preferably at an isosbestic point of the absorption spectrum of oxy-deoxy hemoglobin, otherwise the reflectance measurements are influenced by the oxy-deoxy changes and require correction therefor.
E—Flavoprotein Concentration
In order to determine the metabolic state of various tissues in-vivo it is possible to monitor the fluorescence of another cellular fluorochrome, namely, Flavoproteins (Fp). Referring to FIG. 13(b), Fp absorbs light at wavelengths of about 410 to about 470 nm and fluoresces at wavelengths of about 500 nm to about 570 nm. The Fp level can thus be measured using Fp Fluorometry. The conceptual foundations for Fp Fluorometry were established in the late 1960's and were published in several papers as will be referenced hereinafter. Simultaneous monitoring of NADH and Fp from the same tissue provides better interpretation of the changes in energy production and demand.
Chance et al., 1971 had used a time-sharing fluorometer to record intracellular Redox State of NADH and Fp. They showed a very clear correlation between the two Chromophores to changes in O2 supply to the perfused liver. Using a time sharing fluorometer reflectometer we had shown the simultaneous monitoring of NADH and Fp from the surface of the rat's brain (Mayevsky, 1976). The kinetics of the responses to anoxia or decapitation were identical for the NADH and Fp indicating that the NADH signal comes from the same cellular compartment as the Fp—the mitochondrion.
The five tissue viability parameters described above represent various important biochemical and physiological activities of body tissues. Monitoring them can provide much information regarding the tissues' vitality. In general, the more parameters that are monitored from the tissue the better and more accurate an understanding of the functional state of the tissue that may be obtained.
There are several techniques that relate to the simultaneous in-vivo measuring of multiple parameters in certain tissues, which can be used for the various pathological situations arising in modern medicine.
The prior art teaches a wide variety of apparatuses/devices which monitor various parameters reflecting the viability of the tissue, for example, in U.S. Pat. Nos. 4,703,758 and 4,945,896.
A particular drawback encountered in NADH measurements is the Haemodynamic Artifact. This refers to an artifact in which NADH fluorescence measurements in-vivo are underestimated or overestimated due to the haemoglobin present in blood circulation, which absorbs radiation at the same wavelengths as NADH, and therefore interferes with the ability of the light to reach the NADH molecules. The haemoglobin also partially absorbs the NADH fluorescence. In particular, a reduction of haemoglobin in blood circulation causes an increase in fluorescence, generating a false indication of the true oxidation reduction state of the organ. U.S. Pat. No. 4,449,535 teaches, as means to compensate for this artifact, the monitoring of the concentration of red blood cells, by illuminating at a red wavelength (805 nm) simultaneously and in the same spot as the UV radiation required for NADH excitation and measuring the variation in intensity of the reflected red radiation, as well as the fluorescence at 440-480 nm, the former being representative of the intra-tissue concentration of red blood cells. Similarly Kobayashi et al (Kobayashi et al, 1971) used ultraviolet (UV) illumination at 366 nm for NADH excitation, and red light at 720 nm for reflectance measurements. However, U.S. Pat. No. 4,449,535 has at least two major drawbacks; firstly, and as acknowledged therein, using a single optical fiber to illuminate the organ, as well as to receive emissions therefrom causes interference between the outgoing and incoming signals, and certain solutions with different degrees of effectiveness are proposed. Additionally since the same optical fiber is utilized for transmission of excitation light and for transmission of the collected light the excitation and the collection point is the same one. This imposes relatively low penetration depth as can be learned from the paper of Jakobsson and Nilsson (Jakobsson and Nilsson, 1991).
Even though both radiation wavelengths are incident on the same spot, since detection is also at the same point, effectively two different elements of tissue volume are being probed since the different radiation wavelengths penetrate the tissue to different depths. This results in measurements that are incompatible one with the other, the blood volume measurement relating to a greater depth of tissue than the NADH measurement. Therefore, the device disclosed by this reference does not enable adequate compensation of NADH to be effected using the simultaneous, though inappropriate, blood volume measurement. There is in fact no recognition of this problem, much less so any disclosure or suggestion on how to solve it. Further, there is no indication of how to measure other parameters such as blood flow rate, Fp level or blood oxygenation level using the claimed apparatus.
In two earlier patents which have a common inventor with the present invention, U.S. Pat. Nos. 5,916,171 and 5,685,313, the contents of which are incorporated herein in their entirety, a device is described that is directed to the monitoring of microcirculatory blood flow (MBF), the mitochondrial redox state (NADH fluorescence) and the microcirculatory blood volume (MBV), using a single source multi-detector electro-optical, fiber-optic probe device for monitoring various tissue characteristics to assess tissue vitality. During monitoring, the device is attached to the fore-mentioned tissue. The probe/tissue configuration enables front-face fluorometry/photometry.
Although U.S. Pat. Nos. 5,916,171 and 5,685,313 represent an improvement over the prior art, they nevertheless have some drawbacks:    (i) The oxidation level of the blood will introduce artifacts, affecting the microcirculatory blood volume (MBV) since these patents do not specify how to compensate for the oxygenation state of the blood in the tissue, i.e., the relative quantities of oxygenated blood to deoxygenated blood in the tissue. As disclosed in International Patent Application PCT/IL01/00906 filed by Applicants, this problem may be overcome by performing the NADH and blood volume measurements at an isosbestic point of the oxyhaemoglobin—deoxyhaemoglobin absorption spectrum.    (ii) There is no facility included for measurement of the oxyhaemoglobin—deoxyhaemoglobin level, i.e. the Blood Oxygenation State, which is also an important tissue viability parameter, worthy of monitoring.    (iii) In these two US patents, the same tissue volume needs to be monitored for all parameters, and the same light source and wavelength is used for the illumination needed for monitoring all three parameters. To measure both the NADH level and the blood flow rate, a relatively powerful UV laser is used having an illuminating wavelength close to the peak of the NADH excitation spectrum. Using a relatively high intensity UV laser illumination source as proposed raises safety issues, especially for long-term monitoring. An additional problem of NADH photo-bleaching arises since high intensity UV laser is used.    (iv) The blood flow measurements impose several requirements on the UV laser source. In particular, the UV laser needs to have a high coherence length and very low optical noise. As discussed in more depth below such lasers at these wavelengths have intrinsic properties which tend to discourage their use in such a device, and are in any case quite rare to come by in the first place.
International Patent Application PCT/IL01/00906, the contents of which are incorporated herein, filed by Applicants further addresses these problems by using two separate illumination radiation sources, one for determination of blood flow rate, and the other for determination of at least one tissue viability parameter such as NADH, blood volume and blood oxygenation state. By separating the light sources, the problem of having a single source capable of satisfactorily enabling the determination of blood flow rate as well as the other three tissue vitality parameters is avoided. This Patent application provides means for simultaneous measuring of tissue oxygenation by reflectometry rather than by measurement of the skew of the NADH or the Fp fluorescence spectra. This method of oxygenation measurement may be of limited use while the fluorescence signals are fading.
In any case, apparatuses that incorporate a laser light source are generally required to comply with relevant laser safety standards, since there is some possibility of harm to tissue from exposure to extensive radiation. The two relevant standards which deal with exposure of human tissue to laser radiation are the ANSI Z136.1-2000 “American National Standard for Safe Use of Lasers” and the IEC60825-1-1994 International Standard called “Safety of laser products”.
These standards define the Maximum Permissible Exposure (MPE) values. These standards relate to laser irradiation of external tissues such as skin and eye and not of the internal organs, in contrast to typical applications of the present invention. Still they are the only known, well established references to safe irradiation values for tissues, and any laser device that is intended to perform nondestructive measurements should comply with these in the absence of a more appropriate full damage test being performed on specific tissue type with specific light irradiation.
Both the above standards permit a maximum of 1 mW/cm2 irradiance at UVA spectral region (315-400 nm) for exposure time larger then 1000 sec. This requirement implies a severe limitation on the light intensity emitted by the distal tip of the fiber optic probe, particularly when shorter wavelength, higher intensity radiation is used. Both these standards address eye and skin exposure. Due to the fact that no specific standard exists for laser exposure to internal organs, these standards have been adopted herein as the applicable standards. This approach was supported by the American FDA (Premarket Notification K992529).
There has been a tendency to reduce the total amount of light sources that are incorporated in medical devices designed for tissue vitality measurements, which generally results in a simplified design, lower costs and increased reliability. Therefore this has led to the search for a special light source that may be used for as many parameters as possible, and resulted in the evolution of special expensive low noise UV light sources for Doppler measurement. Measurement of Laser Doppler at UV wavelengths raise additional safety aspects that significantly complicate the device. On the other hand, recent developments in solid state light sources enable improved design of compact and inexpensive medical devices which may be based on multiple light sources.
In PCT/IL 01/00900 to Applicant, the contents of which are incorporated herein, an apparatus is described for monitoring a plurality of tissue viability parameters of a substantially identical tissue element, in which a single illumination laser source provides illumination radiation at a wavelength such as to enable monitoring of blood flow rate and NADH or flavoprotein concentration, together with blood volume and also blood oxygenation state. In preferred embodiments, an external cavity laser diode system is used to ensure that the laser operates in single mode or at else in two or three non-competing modes, each mode comprising a relatively narrow bandwidth. A laser stabilisation control system is provided to ensure long term operation of the laser source at the desired conditions.
In the desire to avoid unnecessary complication of the device due to multiple light sources, the developers search for a single light source that would provide adequate excitation light for all parameters. This resulted in the evolution of a special expensive low noise UV light sources for Doppler measurement.
Measurement of Laser Doppler at UV wavelengths raises additional safety aspects that significantly complicate the device. However, recent developments in solid state light sources now enable embedding several light sources in a relatively simple device without imposing excess complications to the device.
In these prior art publications in which multiparametric measurements are conducted, the illuminating radiation is provided at a single location, and great care is taken that the same tissue volume, or at least the same tissue layer is the subject of the monitoring, and thus one or more detection fibers have to be strategically located in relation to the illuminating fiber to achieve this goal. In the present invention, there is no imperative need for the same tissue volume or layer to be monitored, and in fact each parameter may be monitored separately on a different part of the same organ. This is because the entire organ is affected substantially equally by the pathological condition, that is the body compensatory mechanism is affecting the organ in substantially the same way thus, the apparatuses, systems and methods used in the prior art for multiparametric monitoring according to the present invention are not necessarily suitable for the purposes of the prior art apparatuses, systems and methods.
It is an aim of the present invention to overcome the above deficiencies in the prior art.
It is another aim of the present invention to provide a multiparametric apparatus, system and method for the diagnosis of metabolic emergency state based on multiparametric monitoring.
It is another aim of the present invention to provide such a device or apparatus that conforms to the relevant laser safety standards.
It is another aim of the present invention to provide such a device or apparatus that is of a convenient size, weight and power consumption such as to enable the same to be portable and/or installable within regular operating theaters.
Other purposes and advantages of the invention will appear as the description proceeds.